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According to the NACE 2002 Cost of Corrosion impact report published with assistance from the Federal Highway Administration, it is estimated that the direct yearly cost of corrosion is around 3% of total GDP, or over 763 BILLION dollars per year. Installing new infrastructure is always a costly endeavor, and understanding the conditions of the soil the infrastructure is being installed in is critical to maximizing the lifespan of your assets.
Here at SoilTestsLab we want to help you maximize your material lifespan, and stop early failures that could have been prevented with a little more knowledge.
In general, the corrosion rate of metals in soil depends on the electrical resistivity, the elemental composition, and the oxygen content of the soil.
Different materials fail under different conditions. This is why we offer the Full Corrosion Suite, which will test for all of the major contributors to galvanic attack. Each material has its benefits and drawbacks and it is important to know how the soil chemistry will impact your specific materials. SoilTestsLab also offers Corrosion Control Recommendation Reports. We have a specialized engineers that will let you know exactly what your soil chemistry is, and how different materials will perform.
The Full Corrosion Suite tests for:
Soil Resistivity - Resistivity is the biggest data point for determining corrosivity. Corrosion is just one big electrochemical process, therefore increasing the soils resistance to electrical current, also increases the metals ability to resist corrosion. The opposite of this is true as well. The less resistive a soil is the more corrosive it will be to buried materials.
pH - The pH level of soil drastically effects the corrosion rate of steel, iron, copper and aluminum alloys. Different materials have vastly different performance outcomes under acidic or alkaline environments. It is important for material selection to understand the pH of the soil before installing underground infrastructure.
Sulfates - Sulfate levels in soil effect the corrosion rate of concrete and concrete encased metals. Sulfate-induced corrosion is driven by a combination of electrochemical factors, passive layer disruption, formation of acidic conditions (like sulfuric acid), and microbiologically induced corrosion through sulfate-reducing bacteria. Although sulfates tend to be less aggressive than chlorides in initiating corrosion, they can still significantly accelerate the degradation of metals, especially in acidic or anaerobic environments.
Chlorides - Elevated Chloride levels contribute to accelerating corrosion rates of concrete encased steel (Rebar), as well as just about all metals. Chlorides disrupt the thin protective oxide layer that forms on the surfaces of metals, which leads to corrosion. Chlorides also create tiny anodic regions (active corrosion spots) that dissolve the metal. This process is called “Pitting.” Additionally, Chlorides increase electrochemical activity, and alter the local environment to become more acidic and reactive.
Ammonium - Elevated ammonium levels contribute to the formation of acidic environments when mixed with water. It also contributed to corrosion via the creation of corrosive ammonium salts, stress corrosion cracking in metals like copper alloys, and increases the conductivity of aqueous solutions.
Nitrates - Nitrates can promote corrosion by forming nitric acid, participating in electrochemical reactions, or reducing to more corrosive species like nitrites or ammonia.
Sulfides - Sulfides accelerate metal corrosion through several mechanisms, including the formation of corrosive metal sulfides, promotion of localized corrosion, induction of stress corrosion cracking, and most importantly can indicate the presence of sulfate-reducing bacteria. (SO₄²⁻+organic matter→S²⁻+CO₂)
Reduction-Oxidation Potential (REDOX) - A positive redox potential indicates that the environment is relatively oxidizing. This means that there is a tendency for substances in the environment to be in their oxidized states rather than their reduced states. Sulfate-reducing bacteria thrive in reducing (anoxic) environments where the redox potential is negative. Positive redox values are not conducive to SRBs because these bacteria require low or negative redox conditions to reduce sulfate (SO₄²⁻) to sulfide (H₂S).
Soil Corrosivity Testing